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From: jseigh <jseigh_es00@xemaps.com>
Newsgroups: comp.lang.c++
Subject: Re: smrproxy v2
Date: Tue, 29 Oct 2024 07:27:40 -0400
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On 10/29/24 00:38, Chris M. Thomasson wrote:
> On 10/28/2024 6:17 PM, jseigh wrote:
>> On 10/28/24 17:57, Chris M. Thomasson wrote:
>>> On 10/28/2024 4:45 AM, jseigh wrote:

>>
>> fwiw, here's the lock and unlock logic from smrproxy rewrite
>>
>>      inline void lock()
>>      {
>>          epoch_t _epoch = shadow_epoch.load(std::memory_order_relaxed);
>>          _ref_epoch.store(_epoch, std::memory_order_relaxed);
>>          std::atomic_signal_fence(std::memory_order_acquire);
>>      }
>>
>>      inline void unlock()
>>      {
>>          _ref_epoch.store(0, std::memory_order_release);
>>      }
>>
>> epoch_t is interesting.  It's uint64_t but handles wrapped
>> compares, ie. for an epoch_t x1 and uint64_t n
> 
> Only your single polling thread can mutate the shadow_epoch, right?
> 

Yes.  It's just an optimization. The reader threads could read
from the global epoch but it would be in a separate cache line
and be an extra dependent load.  So one dependent load and
same cache line.